This invention relates to a lapping tape, and more specifically to a lapping tape adapted for superprecision finishing of magnetic heads and the like.
The term "tape" as used herein means any of narrow sheets, ribbons, and other similar thin pieces, long or short.
Lapping tapes are in use for the final finishing of magnetic heads, magnetic disks, and other precision machined parts. For example, the tapes are used to precision polish magnetic heads for fine adjustments of their surface characteristics before their shipment from the manufacturing plants. Also, they are employed to lap and finely polish the magnetic heads already in service periodically so as to maintain their magnetic recording-reproduction characteristics which would otherwise deteriorate with scratches and other damages due to friction with magnetic tapes or disks.
Nevertheless, the existing lapping tapes often produce localized deep bruises or a multitude of long scratches on the work surfaces to mar their characteristics. There has been no lapping tape, to our knowledge, that is totally immune from this trouble.
Lapping tapes of the character are made by dispersing abrasive particles in a binder and applying the dispersion to a base of plastic, metal, or other film, sheet, disk or the like, forming an abrasive coat thereon. Generally, for high precision finishes, coarse particles cannot be used and instead abrasive particles of smaller diameter are employed. Such fine particles, however, too easily aggregate for thorough dispersion. They simply scatter in the resulting abrasive layer and form tiny islands on the lapping tape surface, with consequent localized deep bruises and a large number of general scratches on the work surface. Even a lapping tape claimed to be the highest in performance among the tapes currently available still presents this problem, as is evident from a practical example given below.
Recently a cleaning tape suited for the cleaning of magnetic heads was taught by Japanese Patent Application Publication No. 60725/1987. The tape is obtained by coating a base with an abrasive coating composition prepared by kneading abrasive particles and an extender together with a binder. To be more specific, a particulate nonmagnetic abrasive (.alpha.-iron oxide or the like), less than 9 on the Moh's scale and from 0.2 to 2.0 .mu.m in particle size, and magnetic iron oxide particles as an extender in an amount of at least 60 percent by weight of the abrasive amount are used. These powders, mixed with a binder, are applied to a base. The resulting tape has a surface roughness, in terms of centerline mean roughness, between 0.04 and 0.1 .mu.m. It has, however, been found that despite the description to the contrary in the literature the particulate magnetic abrasive is too coarse in particle size and the resulting surface is too rough to achieve the intended effects. The proposed technique is, after all, of the manufacture of a cleaning tape that is outstandingly effective in removing abraded dust of the magnetic coating of magnetic tapes from the magnetic head. Experiments have revealed that the tape fails to attain a satisfactory grinding effect as a lapping tape and is also unable to preclude scratching by itself. For the reasons stated the advent of a lapping tape has been awaited which would achieve a satisfactorily high grinding efficiency and yet produce no scratch or deep flaw on the workpieces such as magnetic heads.